Presently, the United States Department of Food Safety and Inspection Services (FSIS) spend over half a billion dollars annually on meat, poultry, and fish inspections for bacterial contaminants. Broadly, the inspections are used to determine the cleanliness of the work area and to detect pathogenic microbes in foodstuffs. Ingestion of pathogenic microbes can result in food poisoning when the microbes are inadvertently packaged into supermarket goods. One example of a pathogenic microbe is Salmonella. Salmonella is a genus of gram-negative bacterium that is a major source of human foodborne illness worldwide. Up to 4 million cases of salmonellosis are reported each year in the United States alone. A number of different serotypes of pathogenic Salmonella are known, the most common of which are S. typhimurium and S. enteriditis. Typically, salmonellosis is treated with antibiotics. However, antibiotic resistant strains of Salmonella are emerging. Listeria and E. coli are also commonly occurring microbial contaminants. Listeria monocytogenes is a gram-positive bacterium that is a common cause of gastroenteritis. Tests for E. coli are performed as an indication of fecal contamination of food and work areas.
The food industry has tended to test for food contamination at the production and wholesale level only. However, between the time a foodstuff is packaged and consumption occurs, a bacterial pathogen that was undetectable at the wholesale check can multiply and can thus become a health hazard. Contaminated food is increasing in importance for the producer. Bad publicity and product recalls cost the food industry millions of dollars each year.
Currently, the assay systems used at the wholesale and production level require specialized training and equipment, are time consuming, and are not very sensitive to the presence of small numbers of pathogenic bacteria. To assay for suspected bacterial contamination, a culture is obtained using a sample of the food or from the workplace that is suspected of being contaminated in order to increase the amount of detectable substance (suspected bacterial contaminant). Culturing may require up to 48 hours. Then, the cells grown in the culture are lysed to produce a lysate. Historically, assaying for pathogenic bacteria has been done using antibodies in an immunoassay for detecting bacterial proteins in the lysate. In recent years, some companies have used a polymerase chain reaction (PCR) based methods to replicate microbial genetic material for use in detection assays. The isolated genetic material is multiplied and identified in separate steps. The PCR detection system also requires hours rather than minutes to perform. Testing is performed at the time of or before shipping a product to the supermarket. A simple, sensitive, and rapid method for detecting food contamination is required both for testing at the wholesale level and at the retail level.
Detection devices are also needed at the retail level to protect the consumer. Testing apparatus useful at the wholesale level generally is not useful at the retail level for various reasons. First, most wholesale level tests require technical skills not often practiced by the typical consumer. Second, when a product remains on the shelf before purchase, contaminant levels can increase, especially if the temperature of the product is not appropriately controlled. During the time the food is in transit, bacterial growth can occur. Methods and devices for detecting microorganisms in food at the retail level have been set forth. While tests have been developed for the retail market, they have failed to be adopted. Colorimetric detectors of changes in ionic content, for example pH, of the liquid or material surrounding the food product have been used on or incorporated into retail packaging such as illustrated in U.S. Pat. Nos. 4,746,616 and 5,053,339, the disclosures of each of which are incorporated herein by reference. Antibodies have also been coupled to calorimetric labels for detection of contaminates such as illustrated in U.S. Pat. Nos. 5,306,466 and 5,869,341, the disclosures of each of which are incorporate herein by reference. None of the aforementioned are sufficiently specific and sensitive to meet the needs of the current marketplace.
A means for specifically and sensitively detecting the presence or absence of at least one pathogenic microorganism in potentially contaminated food products at the retail level is needed.